[core] don't assign clip IDs to tiles that aren't rendered

src/mbgl/algorithm/generate_clip_ids_impl.hpp

@@ -15,6 +15,10 @@ void ClipIDGenerator::update(Renderables& renderables) {
     for (auto it = renderables.begin(); it != end; it++) {
         auto& tileID = it->first;
         auto& renderable = it->second;
+        if (!renderable.used) {
+            continue;
+        }
+
         renderable.clip = {};
         Leaf leaf{ renderable.clip };
 
@@ -58,6 +62,9 @@ void ClipIDGenerator::update(Renderables& renderables) {
         uint8_t count = 1;
         for (auto& pair : renderables) {
             auto& renderable = pair.second;
+            if (!renderable.used) {
+                continue;
+            }
             renderable.clip.mask |= mask;
 
             // Assign only to clip IDs that have no value yet.

src/mbgl/renderer/render_tile.hpp

@@ -24,6 +24,7 @@ class RenderTile {
     Tile& tile;
     ClipID clip;
     mat4 matrix;
+    bool used = false;
 
     mat4 translatedMatrix(const std::array<float, 2>& translate,
                           style::TranslateAnchorType anchor,

src/mbgl/style/source_impl.cpp

@@ -70,11 +70,13 @@ void Source::Impl::startRender(algorithm::ClipIDGenerator& generator,
 void Source::Impl::finishRender(Painter& painter) {
     for (auto& pair : renderTiles) {
         auto& tile = pair.second;
-        painter.renderTileDebug(tile);
+        if (tile.used) {
+            painter.renderTileDebug(tile);
+        }
     }
 }
 
-const std::map<UnwrappedTileID, RenderTile>& Source::Impl::getRenderTiles() const {
+std::map<UnwrappedTileID, RenderTile>& Source::Impl::getRenderTiles() {
     return renderTiles;
 }
 

src/mbgl/style/source_impl.hpp

@@ -63,7 +63,7 @@ class Source::Impl : public TileObserver, private util::noncopyable {
                      const TransformState&);
     void finishRender(Painter&);
 
-    const std::map<UnwrappedTileID, RenderTile>& getRenderTiles() const;
+    std::map<UnwrappedTileID, RenderTile>& getRenderTiles();
 
     std::unordered_map<std::string, std::vector<Feature>>
     queryRenderedFeatures(const QueryParameters&) const;

src/mbgl/style/style.cpp

@@ -404,6 +404,7 @@ RenderData Style::getRenderData(MapDebugOptions debugOptions) const {
             auto bucket = tile.tile.getBucket(*layer);
             if (bucket) {
                 result.order.emplace_back(*layer, &tile, bucket);
+                tile.used = true;
             }
         }
     }

test/algorithm/generate_clip_ids.test.cpp

@@ -6,6 +6,7 @@ using namespace mbgl;
 
 struct Renderable {
     ClipID clip;
+    bool used = true;
 
     bool operator==(const Renderable& rhs) const {
         return clip == rhs.clip;

test/api/annotations.test.cpp

@@ -419,3 +419,32 @@ TEST(Annotations, VisibleFeatures) {
     features.erase(std::unique(features.begin(), features.end(), sameID), features.end());
     EXPECT_EQ(features.size(), ids.size());
 }
+
+
+TEST(Annotations, DebugEmpty) {
+    // This test should render nothing, not even the tile borders. Tile borders are only rendered
+    // when there is an actual tile we're trying to render, but since there is no annotation, we
+    // should not render them.
+    AnnotationTest test;
+
+    test.map.setStyleJSON(util::read_file("test/fixtures/api/empty.json"));
+    test.map.setDebug(MapDebugOptions::TileBorders);
+    test.map.setZoom(1);
+
+    test.checkRendering("debug_empty");
+}
+
+
+TEST(Annotations, DebugSparse) {
+    // This test should only render the top right tile with the associated tile border, but no other
+    // tiles because they're all empty.
+    AnnotationTest test;
+
+    test.map.setStyleJSON(util::read_file("test/fixtures/api/empty.json"));
+    test.map.setDebug(MapDebugOptions::TileBorders);
+    test.map.setZoom(1);
+    test.map.addAnnotationIcon("default_marker", namedMarker("default_marker.png"));
+    test.map.addAnnotation(SymbolAnnotation { Point<double>(10, 10), "default_marker" });
+
+    test.checkRendering("debug_sparse");
+}